such filter devices are generally used as dialyzers, hemofilters or ultrafilters. The filter devices generally consist of a casing in the form of a tubular section with end caps in its end areas. A tubular fiber bundle which functions as a membrane is usually arranged in the casing so that a reliable seal is provided between the first flow space formed by the fiber cavities and a second flow space surrounding the membrane on the outside.
One problem with the design of the inflow and/or outflow chambers connected to the first flow space, i.e., to the hollow fiber bundle, is how to distribute the liquid so that it is apportioned evenly to the individual fibers of the hollow fiber bundle, and so that dead zones in the distribution of liquid are avoided.
There are known dialyzers where the inlet of the chambers connected to the hollow fiber bundle is arranged axially, with the axis of the flow channel running approximately through the mid point of the hollow fiber bundle. This generally yields the disadvantage that use of the fibers varies greatly, and at the same time there are areas where the flow velocity is approximately zero (dead zones). After finishing a dialysis treatment, such dead zones are the areas where the patient's blood remains behind. In addition, there is a great difference between the flow velocity in the inlet and that in the fibers. The blood is exposed to a stress situation due to the resulting velocity gradient.
Unexamined German Patent DE-OS 26 46 358 describes a filter device where the end caps have a tangential inlet and the blood is carried in a channel in circulation through the ends of the hollow fibers. Blood flows tangentially through the hollow fiber ends. To achieve the most uniform possible distribution of liquid, only the areas of the casting compound in overflow circulation are provided with hollow fibers, while the rest of the core area does not have any fibers. This achieves uniform loading of the fibers but also results in a relatively low capacity or suboptimal utilization of the filter device on the whole due to the lack of hollow fibers at the center of the casing. To achieve a uniform rate of circulation of blood in the channel, the cross-sectional area of the channel in one embodiment decreases in the direction of flow.
It has also been proposed that the inlet be located parallel to the plane of the fiber ends and that the medium should change directions by 90 degrees in the end area of the inlet. Due to the small amount of available space and the manufacturing restrictions due to the injection molding process, only an abrupt change of directions is possible in general, but that would constitute a considerable burden on the blood.
The object of the present invention is to improve upon a generic filter device so that the transfer of blood from the inlet into the fibers is accomplished at a low load and the fibers are loaded uniformly.